Shaft Sinking

R M Bhattacharjee

Shaft sinkingWhy shaft is required?Why shaft sinking so critical?What factors influence selection of shaft?What are the hazards of shaft sinking?What are the major operations of shaft

sinking?

Why shaft is required?

To provide an entry to mineral deposit at deeper horizon

To ensure safe travel of men to place of work underground

To provide passage for ventilating air of required quantity

For transport of material, mineral or machines

To provide passage for taking down sources of energy , electrical, pneumatic, or hydraulic and communication system

To act as sump at pit bottom

Why shaft sinking is a critical operation?

Shaft is the life line of a mineIt should remain serviceable throughout the

entire life span of a mineStability and integrity of shaft and its fittings

are safety criticalShaft sinking involves high capital

expenditure – has high impact on costShaft capacity determines the economics of

mine

Hazards of shaft sinking

Stability of ground or sidesNoxious or toxic gasesTemperature and humidityFall from heightSlip / trip and fallHit by objects / machines / buckets / grabs

etcRestricted work placeBlasting projectilesWater – drowning

What factors influence selection of shaft?

Installation from surface or undergroundVertical or inclinedTonnages to be hoistedSize of mining equipment to be loweredAmount of water to be handledVentilation requirementThe type of ground through which shaft is to

be sunk throughPosition of shaft in relation to ore body

Location of shaft

Position wrt deposit’s geometryProduction shaft – at geometrical work load

centre of depositOre handled in tonne-km should be equal, as

far as possible, from all sidesFor flat deposit, protection pillar around shaftFor steeply dipping deposits, on footwall side

of ore body

Location of shaft

Position wrt surface topographyShaft collar at least 5 m above recorded HFLAway from places of public utility and water

bodies Within an easy access to infrastructure

facilitiesEnough space around to establish necessary

facilities and construction

Location of shaft

Position wrt geological disturbances, water table and ground conditionType of strata through which shaft will pass

throughPassing through geologically disturbed strata

should be avoidedLoose ground, water bearing strata, mud and

running sand areas offer difficulties and require special treatment

SHAFT SITE SELECTION

SINKING CYCLE

DrillingBlastingMuckingHoistingSupport or shaft liningAuxiliary operations

DewateringVentilationLightingShaft centering

SINKING METHODSORDINARY

METHODSSPECIAL

METHODSPiling

Wooden Steel Concrete

Caisson Pneumatic Without pumping With pumping

• Freezing

• Grouting

Cement

Clay

Chemicals

• Shaft drilling & Boring

General arrangements for shaft sinking

SEQUENCE OF SINKING OPERATION - DRILLING

Sinkers – 32-38 mm dia holesShaft jumbos (with no. of drifters) – 40-55mm

dia holesHole length – 1.5 to 3 m for sinkers /upto 5m

for shaft jumbosDrilling pattern – Wedge cut / pyramid cut /

step cutWedge cut popular in rectangular shaft

whereas pyramid cut for circular shaftStep cut where make of water is high and x-

section is large

SEQUENCE OF SINKING OPERATION - DRILLING

No. of holes depend on hole dia, shaft dia, type of strata

N = 2.55A + 22A is cross sectional area in m2

For circular shaft, in holes are drilled 3 to 5 concentric circles

Ratio of holes 1:2:3 or 1:2:3:4:5

Drill jumbo

Advantage of drill jumbo:Enhanced Sinking rate and productivityReduction in cost of sinkingReduced human and machine populationSmall crews – better management

LimitationHigher capital cost of rigs and sparesSkilled maintenance and operationKibble winder and opening through working

stage – to be matched with jumbo dimension

Wedge cut

Pyramid cut

DrillingBy pneumatic drill – rotary percussiveAir pressure > 80 psiHollow drill steels fitted with detachable bits

tipped with tungsten carbideShape of drill bit depends on strength of rockNo. of drills used / jumbo

Arrangement of holesConcentric ringsCut holes at an angle towards the centreSumpers / Inner easers / Outer Easers / Side

holes or trimmers or flankersAngles of holes reduces towards the outer

rings and side holes are vertical

Pyramid cut with jumbo

Step cut

Drilling with shaft jumbo

Longer hole blasting

Earlier holes were about 4 feet longNow holes of 4 to 5 meter length are drilled

by jumbosCut holes of 3.5 inches to 7.9 inches are

drilled to provide initial free faceEmulsion explosives are less expensive,

faster in loading, providing full borehole coupling, reduces drilling time and results better fragmentation

BlastingHigh density water resistant explosive such

as Nitro-glycerin based explosive Aluminum based water gel explosiveWater gel slurriesUse of emulsion explosives with boosters and

NONEL detonators

Blasting

Weight of explosives per cubic meter of rock blasted depends on Nature of rockStrength of explosiveDegree of fragmentation requiredDepth of pull

No. of holes varies from 80 to 100Weight of explosives per hole

Total explosivesNo. of holes750 – 1 kg per hole of 6 ft

BlastingWater or sand clay mixture as stemmingStemming used – 3:1 sand clay mixture for

dry shaft or sand alone in wet shaftSeries – parallel connectionsBlasting cable from surfaceMain shot firing cable suspended from

surfaceMust be able to support its own weight2 core cable or 2 separate single core placed

on opposite sidesPVC insulated single wire armoured and

seathedCoiled on drum

Removal of debrisDifficulties

Presence of waterLimited spaceTime required for installing mucking

equipmentOccupies about 50-60% of sinking cycle

Mucking efficiency depends onSize of rock fragmentsHoisting depthShaft cross sectionWater inflow rate

Removal of debrisBroken debris loaded into kibbles or bowks,

manually or mechanicallyMore than one kibbles are used at shaft

bottomMechanical loaders use compressed air

operated grabThe grab consists of a ring of powerful steel

jaws or fingers which can be opened or closed by comp air operated by a man at shaft bottom

The grab hangs from a control tower or frame mounted on the permanent lining

The tower can be raised or lowered by a winch at the surface

Lashing and muckingLashing unit is a mechanical device

incorporating hoisting, slewing and radial traversing mechanism for handling of the cactus grab

Types of shaft muckerArm loaders like cactus grab / cinderman

mucker / backhoe muckerRocker shovel Scraper

Cinderman mucker

HoistingHoisting / Lowering of men, material and

muck by temporary hoist, headgear and other attachments

Main componentsHead gear with pulleys

Substantial construction Capable of withstanding load upto 120-150 te Compact to enable erection of permanent structure Bolted construction for easy dismantling Central pulley for sinking rope Two side pulleys for walling platform ropes All three ropes are locked coil, non-spinning type Platform ropes also act as guide ropes for rider to

keep the kibble steady in the shaft when being raised or lowered

HoistingHoisting / Lowering of men, material and

muck by temporary hoist, headgear and other attachments

Main componentsRider

Permanent guide ropes are not possible to be installed while sinking in progress

When a walling is used, the scaffold ropes with an appliance RIDER may act as guide ropes for the kibble above the point where scaffold is suspended in the shaft

Davis and Barker’s Cone sinking rider is well known The vertical limbs should be long enough to prevent

canting of the rider

HoistingHoisting / Lowering of men, material and

muck by temporary hoist, headgear and other attachments

Main componentsRider

At the centre of the cross bar of the rider, a circular block with hole large enough for the detaching hook to pass through to prevent over winding

Mounted loosely on the winding rope is a collapsible spider or guide sleeve which fits into the central hole (and remains there, so keeping the rope steady) when the rider is at rest on the walling scaffold and the kibble suspended from the spring hook, below that level

When the kibble is above the scaffold, rider is lifted by the carrier cone inserted in the bridle chain, which engages in the underside of the block

GENERAL ARRANGEMENTS FOR SHAFT SINKING

Walling platformUsed for construction of side wallsDia of the platform is slightly less than dia of

the shaftSuspended by two ropes, which also act as

guide ropes for the kibbleEach rope carries two bridle chains secured

by shackles to four bolts A no. of rubber rings, supported by clamps,

are secured to each rope to relieve the impact of ride

The platform has a central opening for passage of the kibble

To keep the platform steady when persons are at work, four stout iron keys or bolts are pushed out to rest on the top of finished section of walling or in holes left in walling

Walling platformDuring sinking, scaffold is suspended within

50 ft above shaft bottomThe scaffold should be as close to the shaft

bottom to guide the kibbleWhen blasting, scaffold should be raised

temporarilyBesides being used for walling, scaffold also

provides protection against falling materialsIt may also be used as emergency means of

exit in case of anything wrongNo of rope ladders are attached to the

scaffold reaching to the bottom

Walling Platform

SEQUENCE OF SINKING OPERATION

SEQUENCE OF SINKING OPERATION

GENERAL ARRANGEMENTS FOR SHAFT SINKING

GENERAL ARRANGEMENTS FOR SHAFT SINKING

GENERAL ARRANGEMENTS FOR SHAFT SINKING

GENERAL ARRANGEMENTS FOR SHAFT SINKING

Temporary support of sides

Temporary support of sidesWhen one round of shots fired and debris

removed, support of sides are necessaryDone by system of steel curbs or skeleton ring

with close lining of wooden backing deals or steel plates

Mild steel curbs of 4-5 inch deep, 1 inch thick and 6-8 ft long segments with overlap and joined by bolts or fish plates

Each curb is suspended from the one above by 6-8 s-shaped steel hooks or hangers

Every third or fourth ring must be additionally supported on plugs placed into holes horizontally drilled into the strata

Wooden backing deals about 5-6 ft long are placed close together behind the curbs and each deal is provided with its own wooden wedge to tighten the structure

Temporary support of sides

In all steel arrangements, curbs are channel sections and are butt jointed by fish plates and four steel pegs

Curbs are supported by hangers and are backed by steel plates provided with a hook enabling them to be suspended behind the curbs

Very quick to install and can be reused many times

Temporary supports are removed, section by section, as the permanent lining is built up.

Permanent lining of shaftsTypes of shaft lining

Brick walling – dry shaftsConcrete blocks -Monolithic concrete – Most commonly usedcast iron tubbing – heavily watered shaft

Function of shaft liningTo prevent deformationTo prevent decrepitating due to influence of

atmospheresThickness of lining

Stresses to be resistedNature and strength of material used for lining

Permanent lining of shafts

Stresses on shaft liningCompressive in nature – from outside to inside

of shaftDepends on

Dia of shaftDepth of shaftNature of strataPresence of water

Tensional stress may be developed locally due to presence of faults, cavities, or other weaknesses

Permanent lining of shafts – Brick walling

Suitable for compact and fairly dry strata, where stresses are not high

14 inch walling is adequateOften 9 inch walling is sufficientLime mortar or cement mortar is used

Walling curbEach length of brick work is built up from a

walling curb laid on a specially prepared bed of strong ground

The curb may be of cast iron or concreteCast iron curb is a L shaped ring, 10-18 inch

wide and ¾ to 1 ½ inch thick, divided into number of segments

Ends of segments have vertical flanges, for bolting adjacent segments

Curb bed must be specially prepared, smooth and level

Curb should be truly circular and horizontalIts centre should coincide with the shaft

centre

Cast iron walling curb

Erection of brick wallingWhen approaching the site of the curb, size

of shaft is gradually increased or laid back about 2 ft all round

Inside dia of the curb is the finished dia of the shaft

Walling is built up from the curb, beginning about 2 ½ to 3 ft thick and gradually decreasing to normal thickness

To maintain verticality, side plumb lines are suspended from the curb above

Temporary supports are removed in sections as walling ascends

All spaces behind walling are packed solid with ashes, broken rocks or bricks or with concrete

Walling a shaft

Erection of brick wallingWhen a length of walling is completed,

sinking is continued at a reduced diameter, in alignment with the inside of walling

Shaft is then widened out to its ordinary size, some 2-3 m below, to leave a strong ledge of stone, as at L, to support the walling

The thicker portion serve to divide the entire shaft wall into separate portions independent of each other, each carrying out its own weight

If ever one portion is collapsed or had to be removed, other parts would not be disturbed

Erection of brick wallingWhen next lower length of walling is built up,

it is continued of the required thickness until it reaches the point W

The front portion of the ledge beneath the last curb is then cut away, a narrow width at a time, but upto the full height, so as to make room for the remainder of the walling

This is called underpinning of the walling curb

Concrete walling curb

In this case, the ground is cut back about 2 ft in

wedge form so as to key the concrete curb into

the strata

To form the curb, to retain the wet or plastic

concrete in position, shuttering is placed

Shuttering (S) are steel sheets, curved to suit the

circumference of the shaft and having angle irons

A riveted to them to enable adjacent segments to

be securely bolted together

Concrete walling curb

At the shaft bottom, each segment of the first

shuttering ring rests on a sleeper

The complete ring, when bolted up, must be

carefully leveled and centered

Small debris of 6 inch height is placed behind the

ring, followed by a layer of sand covered with

brattice cloth

One or more rings of bricks may be laid so that

they may be removed later to enable the length of

the walling to be keyed into the above

Concrete walling curb

Concrete is now placed behind the shuttering

ring

Is well rammed to fill all cavities next to the

strata and prevent formation of air pockets in

finished concrete

The second ring of shuttering is then placed,

centred, leveled and filled up same way

Temporary lining is removed as concreting

procedes

Concrete walling curb

Advantages of concrete curbThey are self supporting and underpinning is

not requiredThey can be applied in any groundLess liable to damage from blasting when

sinking is in progressVery strongLong length of walling can be carried on a

single curb

Monolithic concrete lining

Monolith is a pillar or column consisting of

single stone

Monolithic concrete lining is one built up

with a single mass of concrete instead of

with concrete blocks

Monolithic concrete liningAdvantages

Can be constructed rapidly and at low costHigher Compressive strength (3000-5000 psi)

compared to brick lining (800-1500 psi)The concrete extends right back to solid strata,

filling up all cavities and irregularities and this adds to the rigidity and strength of the lining

It presents a smooth surface to ventilating current

Suitable for water bearing strata owing to its capacity to settle under water , its freedom from joints and its ability to withstand pressure when injecting liquid cement behind to seal off feeders

It can be rendered immensely stronger by steel reinforcement, where necessary

Erection of concrete walling

A round of shots, below the length to be lined, is fired and the broken rock roughly leveled and left in position in readiness for resumption of sinking

First shuttering ring is then truly centered, leveled on sleepers or wooden blocks

A base is prepared for the concrete behind the ring

When the length of shaft to be lined has been sunk and temporarily supported, a concrete curb is built up and shuttering rings are added progressively to retain the plastic cement

Erection of concrete walling

A second ring is addedConcrete is fed from surface via pipe and

armoured hose until the space behind the two rings is nearly full

During filling, concrete is well rammedAll temporary supports are removed in

succession as work proceeds and further rings of shuttering added as required

Shuttering must be left in position until such time concrete is set

To facilitate the removal. Back of the shuttering are cleaned and well greased each time

Erection of concrete walling

When the rising wall reaches the next section of wall above, care is needed to make a good joint

A spl L shaped grouter ring is mounted on the last shuttering ring

When concrete has reached within an inch or two of the top wall, fine grout of sand and cement is poured in to close the gap

Grouter ring is filled to the topWhen grouter ring is removed, the excess

material is dressed off

Erection of concrete walling in water bearing ground

Back corrugated sheets are placed all round the shaft and are held in position by skeleton curbs and wedges

These sheets serve the purpose of temporary lining and also of keeping water away from concrete during walling

At suitable point, where walling is to begin, a temporary water garland is formed to catch water flowing behind back sheeting and is led into pipes from which it is discharged down into the shaft

Erection of concrete walling in water bearing ground

A base is prepared to receive concrete and first ring of shuttering and first length of steel reinforcement are erected

Concreting is now begun, skeleton curbs being removed stage by stage

Further rings of shuttering and steel reinforcement are added

Space behind the back sheeting is filled with clean gravel by removing portions of the back sheeting at intervals

Horizontal relief pipes are laid in the concrete at regular interval, extending through holes in the shuttering

Later on, after removing the shuttering, fine grout of cement and sand is injected to seal behind the back sheeting

Erection of concrete walling in water bearing ground

Cast Iron Tubbing

An alternative method of permanent lining of shaft sunk through heavily watered strata

Mostly associated with freezing process, where there is difficulty in setting of concrete

Tubbing is inserted while the ground is still frozen, so that the sinkers work under dry condition

Later, the ground is allowed to thaw slowly so that water pressure may build up gradually behind the tubbing

Water Ring Garland

Water Ring GarlandCast iron garland is having a channel around its

inner circumference to catch the water draining down the shaft sides

Garland consists of a no. of segments, which when bolted together, form a circle having same dia as finished dia of the shaft

Each segment is an open-topped casting of 18 inch wide, 4 ½ inch deep

One or more of the segments provided with an outlet hole into which is screwed a nipple from which 2 inch dia pipes convey water away to pumps at shaft bottom

To avoid front edge of the space water-ring projecting into shaft space, the walling above the ring is laid back about 4 inch and is brought back gradually to normal dia above 5 ft above

Special Methods of Shaft Sinking

When the strata through which shaft s to be sunk include deposits of loose or unstable ground, such as mud, sand, gravel, or alluvium, or when they contain excessive quantities of water which can not be dealt with by sinking pumps, or when both difficulties occur together, it is necessary to adopt special methods of shaft sinking

Special Methods of Shaft Sinking

Pile sinking or PilingCaisson sinkingFreezingCementation

Piling SystemSuitable for sinking through loose ground

near surfacePiles may be of either wood or steelThe system consists of driving down into

loose ground a circular lining of wooden backing deals, which are called piles

Piles vary in length from 6 ft to 15 ft, are 3 inch thick and 6-8 inch wide

Each pile is shod at bottom with an iron point or shoe

Piles are driven down by heavy mallets , and are placed skin to skin to form a complete circular ring

They are held in place by wooden curbs or rings, placed at intervals of 2 to 3 ft

Piling SystemSuitable for sinking through loose ground

near surfacePiles may be of either wood or steelThe system consists of driving down into

loose ground a circular lining of wooden backing deals, which are called piles

Piles vary in length from 6 ft to 15 ft, are 3 inch thick and 6-8 inch wide

Each pile is shod at bottom with an iron point or shoe

Piles are driven down by heavy mallets , and are placed skin to skin to form a complete circular ring

They are held in place by wooden curbs or rings, placed at intervals of 2 to 3 ft

Piling System

When the piles are driven a short way down, a curb is fitted within them

The ground inside is cut awayThe piles are kept about 2 ft in advance of

the excavationPiles are driven down one by one until hard

ground is reachedA walling curb is then laid and a strong wall

is built up in front of the piles, the space behind suitably packed

Piling SystemEach successive ring of timbering is of

smaller dia than the previous oneIt is necessary to start with larger dia, which

depends on depth of the running ground and dimension of the timber

For a shaft dia of 15 ft, with 8 ft long, 3 inch thick and 6 inch square curbs, starting dia is ?

There is a limit of depth beyond which it would be impracticable to use wooden piling system, as enormous excavation is required

Steel Piling System

Much stronger than wooden pilesCan be driven with much greater force with

piling hammer

Caisson Methods

Suitable for running ground at somewhat greater depths

Three typesSinking drum processForced drop shaft methodPneumatic caission method

Sinking drum process

Sinking drum process

Similar to pilingLining of the shaft is formed in advance of

excavationPiles are replaced by cylindrical drum of

brick work and steel or of RCC, fitted with a steel cutting shoe at its lower end

The brick work is 12-18 inch thick, resting on wooden curb fitted with steel cutting shoe

Other wooden curbs are built into the cylinder at intervals of 3-4 ft, and are tied together by wrought iron rods to increase strength of the structure

Sinking drum process

The drum sinks gradually by its own weight as the shaft is excavated

Further brickwork is added at the topCare must be taken to ensure drum descends

verticallySometimes wooden boards are placed

outside the drum to reduce friction

Sinking drum process

AdvantagesLining is built on surface, where construction

is safest and cheapestDrum acts as permanent lining for finished

shaftCost of temporary timbering is eliminatedWeight and strength of drum sufficient to push

aside boulders etc that would stop timber or steel pile

Sinking drum process

DisadvantagesSometimes difficult to keep the drum verticalSkin friction increases rapidly with depthDanger of drum being sticking altogetherIn running ground, large amount of excess

material is often excavated, resulting in subsidence of surrounding surface and damaging adjacent structuresIt is not advisable to install permanent headgear and winding engines till sinking through loose ground completed

Forced drop shaft method

Forced drop shaft method

Applicable to cases where beds are known to consist of alternate tough and loose ground in which ordinary sinking drum will either refuse to descend or would not sink far enough to prevent excessive quantities of loose material entering the shaft from below cutting shoe

Forced drop shaft method

It consists of jacking or forcing down by hydraulic rams one ( or more) cast iron drums of internally flanged tubbing within a preliminary caisson of brick work or concrete

The brick work caisson may form the walling in the upper part of the shaft

The hydraulic rams re-act against a massive cast iron pressure ring erected on top of brick work caisson, connected by number of stout vertical anchor bolts and guide bolts to a strong anchor ring

Forced drop shaft method

Anchor bolts are embedded in the brick workGuide bolts are close to the inner periphery

to form guide for tubbingPressure and anchor rings are strong to

resist enormous pressure of ramsWhen the tubbing has been forced down,

another ring is added to the top

Forced drop shaft method

AdvantagesMuch greater depth of loose ground can be

piercedDiameter of excavation is not excessiveMore certain method

Pneumatic caisson method

Designed for waterlogged quick sand or mudLower portion of the drum is converted

virtually into a diving bell by means of partition or diaphragm, 6 or 7 feet above the shoe

Compressed air at a pressure exceeding that of the surrounding water is led into the chamber so formed

An airlock is mounted on top of the chamber to permit passage of men and materials

The caisson sinks by gravity

Pneumatic caisson method

Pneumatic caisson method

DisadvantagesWorking in compressed air is injurious to

health – cause caisson sicknessLimiting depth is about 100 ftSlow progress and costlyCompressed air is liable to be vitiatedRelatively higher temp of comp air

Freezing process

Suitable for any kind of heavily watered strata, including quick sands

The process is formation of large cylinder of frozen ground in the centre of which it is possible to sink by ordinary method

No requirement of pumping

Freezing process

Freezing is accomplished by boring a ring of holes through the

permeable strata, slightly outside the size of the shaft and

by circulating through steel tubes in these holes a solution of cold brine which slowly absorbs heat from the ground and progressively lowers its temperature to freezing point

Eventually a temperature well below freezing point is reached in order to obtain an ice wall of sufficient thickness and strength to resist pressure of water in the strata

Freezing process

Four stages of shaft sinking by freezing process:BoringFreezingSinking Thawing

Boring

Number of vertical holes (20-50) drilled at a short distance from the outside circumference of shaft

Verticality is essential to ensure that ice wall is continuous

All the holes are lined with steel tubes, to prevent caving

Lining tubes are withdrawn after inserting freezing tubes

Freezing

Two concentric freezing tubes are inserted in each borehole

An outer tube of 5 inches dia, sealed properly at its base

An inner tube of 2 inches dia open at the lower end and reaching nearly to the sealed end of larger tube

Outer tubes are connected at the surface to a circular main or distribution pipe

Inner tubes are similarly connected to another main

Both mains are fitted with valves and cocks to control circulation of brine

Freezing

Brine is usually a solution of Cacl2

The brine takes up heat during its passage through the tubes

The brine must be sufficiently cooled by refrigerator

Freezing process

Brine circuit

Brine, at a temp of about -20 o C to -50 o C is pumped down the inner tube A and goes to the bottom of hole

It then ascends between inner and outer tubes A & B, extracting heat from the surface

It then passes into a brine tank where it comes in contact with spiral coils of refrigerator or ammonia evaporator

By this the brine is cooled in readiness for passing once again through freezing tubes

Ammonia circuit

Through the coils of the evaporator , refigerating agent or anhydrous ammonia is circulated

It reaches to the bottom of the lowest coil of the evaporator coils as a liquid, but is converted in to gas at the temperature of the brine as it rises through the coil

The heat required for evaporation is taken from the brine, which is thereby cooled

The gaseous ammonia, on leaving the evaporator, passes through an ammonia compressor where it is compressed to about 150 psi, the temperature being about 70 o C

Ammonia circuit

From there, the ammonia passes through an oil separator into the coils of condenser or liquefier

Under the influence of cooling water at atmospheric temperature, it liquefies

It again expands into a gas at the evaporator

Freezing

Circulation of the brine may be carried out in all the boreholes simultaneously

Ice wall will grow slowly around each freezing tube until the cylinders of ice join together

The time required for ice wall to form varies from two to six months, depending on the size, depth of shaft and nature of strata

Sinking

Sinking of shaft through frozen ground is carried by ordinary method

No pumping necessaryIf ice wall is effectively formed, shot firing

may be carried out without restrictionOnly Low freezing explosives must be usedWhere depth is moderate, shaft is timbered

temporarily with steel curbs with backing deals

Permanent lining is built up in sections

Sinking

The upper part of the shaft, above the water level may be lined with brickwork or concrete

From water level down to impermeable strata beneath water bearing strata, a water tight lining is provided by cast iron tubbing backed up by concrete

Cement mortar behind may be prevented from freezing by mixing with water containing 6-7% caustic soda or CaCl2

Sinking

In deep shafts, where pressure to be resisted is very high, permanent lining should be inserted ring by ring backed by concrete as soon as sufficient ground is excavated

Frozen ground is plastic and liable to deformation under great pressure

ThawingWhen shaft has been sunk through wet

ground, freezing may be stopped and ground may be allowed to thaw

Originally thawing was effected by blowing steam through freezing tubes

This caused breakage of freezing pipes, leakage of water and cement through tubbing and unequal distribution of pressure on shaft lining due to irregular thawing

Later, freezing plant was stopped, and brine was heated and circulated through freezing tubes

Shaft was also filled with hot water to ensure thawing of thin cylinder of ice, immediately next to tubbing and so prevent development of local pressure

Thawing

In modern practice, brine is merely warmed and circulated at such temperature and in such a way that thawing begins at the bottom of the tube and progresses gradually top wards

Shaft not being filled with hot waterShaft remains free for thorough inspection

and any defect remedied at once

Cementation

Cementation implies injection of liquid cement through boreholes into strata to fill up any cavities, fissures, cracks, and thereby strengthen and consolidate the strata, rendering it impervious to water

Applicable for firm but fissured water bearing strata where inflow of water would otherwise be excessive and unmanageable

It can be successfully used to seal porous rocks or fissures containing sand and other fine loose material

Not suitable for running sand

Cementation – Pre-silicatization

Certain kinds of porous rocks possess very high frictional resistance to penetration

Their natural porosity allows a considerable inflow of water

This difficulty may be overcome by pre-treating the ground with certain chemicals like silicate of soda and sulphates of alumina

This process is called silicatizationThe ground reacts with the chemicals to form

a gelatinous precipitate of aluminium silicate which has a lubricating action to render the strata more receptive to cement

Stages of Cementation

BoringCementationSinking and walling

Boring

This is usually carried out with heavy percussive compressed air hammer drill

Bore rods are hollowHoles are drilled from within the perimeter of

the shaft on a circle more or less concentric with it

First series of holes are drilled from dry ground, if possible

Some of the holes should be drilled inclined radialy and tangentially so as to ensure interception of all fissures throughout the length

Boring

Each hole is lined with a stand pipe, grouted with cement

Above the top of the hole, fitted with stop valve to control water given off during boring

Boring is continued through valves and stand pipes

As soon as the hole reaches decided depth or encounters fissure containing water , bore rods are withdrawn and stop valves closed

Hole is then coupled with flexible hose to cement pipe range and injected with cement

Cementation

High pressure double acting ram pumps driven by compressed air or electricity used to inject cement

Cement mixing tank, silicate storage tank, sulphate dissolving and storage tank and pipe ranges are required for the cementation operation

Injection

For small fissures one injection of cementation may be sufficient

For large fissures, certain amount of cement is injected and cementation is suspended for few hours to allow setting of cement

Hole is then cleaned by boring and injection repeated until cavity is completely closed

Percentage of cement in mixture varies from 2-50%

Sinking and walling

Ordinary brickwork, cast iron tubbing, reinforced monolithic concrete lining are used with cementation

Staple Shaft / Blind shaft

Vertical shaft connecting two seams or horizons without reaching to the surface

Used for transport of mineral, men and material, and for ventilation

Widely used in horizon mining, for connecting two horizons

In in-seam mining, used in place of long inclined cross measure drifts

Staple Shaft vs Drifts

Advantages of staple shaftsLess time and less cost due to shorter lengthStaple may be located at suitable place free

from geological disturbances etc. where as drift may have to pass through difficult ground

Less costly repairingProtective pillar size is lessLess resistance to ventilation

Staple Shaft vs Drifts

Dis-advantages of staple shaftsDifficult access for repairingInterrupts transportation systemTransport of heavy equipment is difficultLess convenient for transport of men

Driving staple shaft

May be sunk downwards from upper level or raised from lower level

Raising is preferred, if possible, due to ease of mucking , blasted material falls down due to gravity

But raising requires god ventilation, good overhead support

Sinking staple shaft downwards

Similar to that of shaft sinking, may be with smaller dimensions

To accommodate winding pulley and frame work and providing sufficient height for raising and emptying kibbles, vertical excavation is needed

Winding engine installed at upper levelFolding doors and other arrangements

installedShaft sinking and lining proceeds normal

Raising staple shaft upwards

Dividing shafts into number of compartments to provide for debris, ladder way, ventilation

Centre stack method / four compartment staple

Requires great care and experienced person

Raising staple shaft - centre stack method

Three compartmentsLarger middle compartment A for stowage of

debris and also serves as platform for work men

B and C for ventilationIn B, ladder way provided for ascending and

descendingIn C , at the bottom, chute provided for

disposal of excess debrisCentre stack formed by placing pairs of steel

girders and sleepers

Raising staple shaft - centre stack method

For drilling and blasting, top of B & C provided with timber planks from sack girders to top of brick work

Drilling done upwards in concentric ringsBlasted materials fall on planksSupervisor ascends to examine roof and gas,

before allowing work menExcess debris disposed through C

Deepening by blind pit

Shaft Drilling and Boring

Sinking without explosiveEntry of crew is not required during sinkingSafe and economical

Shaft Drilling

Through aquifers or very weak formations, where conventional sinking is difficult, even with special methods, or economically impractical

Based on rotary drilling technology for gas and oil wells

Large dia holes (1.5 – 8m) upto 2000m depth

Shaft Drilling Heavy oil rig with rotary drill and drill string &

bit is usedBit equipped with roller cutters with teeth that

cut rock chips as the bit rotates at the bottomNo. And arrangement of bits vary with size of

holeStabilisers are used to control hole deviationRelatively low speeds for large dia holesVertical thrust varies from soft to harder

formations Drilling mud used to support shaft walls, cools

the drill bit and remove cuttingsDouble walled pipes with reverse circulation is

used for removal of cuttingsWire mesh screens separate cuttings from

drilling fluid, which is recycled

Shaft Drilling

MeritsAll operations carried out from surfaceEffectively deal with ground water, caving and

soft formationsSmooth wall surface at fast penetration rate

achievedLimitations

High capital costDifficulties in drilling through hard strata

Shaft Boring Machinehttp://www.herrenknecht.com/uploads/tx_torrvideoteaser/SBM_D-600_zusammenstelltung_26_02_2011_02_1_02.mp4

Some basic differences in comparison to horizontal tunnelling had to be considered in the development of this new shaft boring machine, which is similar to a conventional tunnel boring machine.

One major challenge was to raise the excavated rock from the shaft bottom and to transport it vertically through the machine up to the transfer point for shaft conveyance.

The solution: The cutting wheel was turned by 90 degrees and the rock is excavated in two consecutive steps.

Shaft Boring Machine

In the first step, the cutting wheel penetrates the rock like a circular saw, thus creating a slit with a depth of 1.5 meters.

In the second step, it rotates around the vertical axis of the machine to cut out the entire shaft profile. In doing so, the cutting wheel not only loosens the rock but also serves as a paddle wheel which transports the muck via integrated channels to the center.

There the material is transferred to a vertical belt conveyor, which transports it to the transfer point for shaft conveyance.

Up to 3 gripper systems brace against the shaft wall and thus stabilize the entire system during the tunnelling procedure.

Shaft Boring Machine

Vertical shaft sinking

Vertical shaft sinking machine

Shaft Sinking Machine consists of two main components – the shaft boring machine, and the lowering units.

The shaft boring machine is lowered into the launch shaft structure and attached firmly to the shaft with its three machine arms.

A rotating cutting drum equipped with chisel tools is attached to a telescopic boom.

This road header excavates and breaks the soil at the base of the shaft. The road header is telescopic, and can swivel up and down or rotate. Hence, the entire cross-section of the shaft plus an overcut can be excavated gradually.

The excavated material is removed hydraulically through a submersible pump and transported to the separation plant on the surface.

Vertical shaft sinking machine

The lower concrete ring of the shaft structure, also referred to as the shaft’s cutting edge, is bevelled and therefore cuts into the surrounding soil underneath.

In addition, the overcut of the road header-like telescopic boom and cutting drum below the shaft’s cutting edge in combination with the bentonite lubrication in the annular gap reduce the frictional forces between the shaft wall and the surrounding soil.

Vertical shaft sinking machine

The lower concrete ring of the shaft structure, also referred to as the shaft’s cutting edge, is bevelled and therefore cuts into the surrounding soil underneath.

In addition, the overcut of the road header-like telescopic boom and cutting drum below the shaft’s cutting edge in combination with the bentonite lubrication in the annular gap reduce the frictional forces between the shaft wall and the surrounding soil.

Vertical shaft sinking machine

On the surface, 3 to 4 lowering units with hydraulic cylinders are attached firmly to the ring-shaped concrete foundation around the shaft.

They are attached to the lower concrete base ring of the shaft structure by steel cables. In this way, the entire shaft structure can be held and lowered in a controlled manner during excavation.

Ring building takes place simultaneously on the surface using prefabricated concrete segments.

The simultaneous working processes (excavation, removal of excavated material, shaft construction, and lowering of the shaft structure) make it possible for VSM technology to achieve high advance rates of up to 5 meters per shift.

Raises

Raising with Jora lift method

Deepening by staple shaft